Fluid filters are commercially available in a variety of styles for filtration of flowing liquids such as water. A typical filter consists of a tank having an inlet for receiving unfiltered liquid, and an outlet for discharging the filtrate. A filtration element is positioned within the tank between the inlet and outlet for removing dirt and particulate matter from the liquid stream passing through the tank.
Filters of this type are in widespread use for filtration of swimming-pool water. Circulation and filtering of pool water is essential to maintain the water in hygienic condition, and to remove dirt particles, leaves, insects and other debris falling on the pool surface.
In a typical home swimming-pool installation, water is drawn from the pool by an electrically driven pump, the outlet of which delivers water under pressure to flow through a purifying filter before being returned to the pool. Systems of this type are typically provided with a strainer or equivalent trap upstream of the pump for removing hair and large particulate materials from the liquid stream before it passes through the pump.
In conventional domestic installations of the type just described, the filtration element is typically a cartridge (or several stacked cartridges) incorporating a filtration material such as diatomaceous earth or a cloth or plastic material which permits fluid flow therethrough, but blocks the flow of particulate materials. In operation, dirt builds up on the filter surfaces which receive the incoming water, and fluid flow through the filter gradually diminishes due to the accumulation of this filter cake. The element must accordingly be periodically removed and cleaned to maintain reasonable flow rates and optimum filtering efficiency.
Cleaning of the filter cartridge is a time-consuming and messy operation which requires unsealing of the tank, removal of the cartridge, washing of the cartridge surface to dislodge accumulated dirt, and reassembly of the system. Most pool owners view this task as an unpleasant duty, and cleaning is often deferred to a point where the filter cartridge becomes badly clogged and is unable to maintain the pool water in sparkling clean condition.
The improvement of this invention largely eliminates the need for frequent dismantling of the filter assembly to clean the filter element. A normally closed air-injection valve is provided in the filter inlet conduit, or at another location on the filter tank, and the valve can be opened to inject air into the flowing stream of unfiltered water. When the need for cartridge cleaning is indicated by either visual inspection or an increase in upstream pressure, the air-injection valve is opened, and an auxiliary filter-tank drain is also opened. Aerated water from the pump then flows against and churns around the clogged surfaces of the cartridge, dislodging dirt and other particulate matter which is exhausted with the water streaming out of the auxiliary outlet without being returned to the pool. The entire aerated-water cleaning cycle requires only a minute or two, and periodic cleaning in this mode greatly extends the time before which dismantling and conventional cartridge washing is required.
Filter-element cleaning using the air-injection valve is very simple, and requires only opening of the injection valve, and an auxiliary-outlet valve or plug. The necessary additional parts for the filter system add little in cost or complexity, and the ease with which the filter can be cleaned insures that the cartridge will be maintained in optimum operating condition.